1. Technical Field
The present invention relates to a power generation unit, an electronic apparatus, a transportation device, a battery, and a method of controlling the power generation unit.
2. Related Art
When a piezoelectric material such as lead zirconium titanate (PZT), quartz crystal (SiO2), or zinc oxide (ZnO) is deformed in response to an external force, electrical polarization is induced inside the material, and positive and negative charges appear on the surface. Such a phenomenon is called a so-called piezoelectric effect. There has been proposed an electrical power generation method of vibrating a cantilever to thereby make a weight repeatedly act on the piezoelectric material, and thus taking out the charge generated on the surface of the piezoelectric material as electricity using such a characteristic provided to the piezoelectric material. For example, by vibrating a metal cantilever having a mass disposed at the tip and a thin plate made of the piezoelectric material bonded thereto, and taking out the positive and negative charges generated on the piezoelectric material due to the vibration, an alternating current is generated. Then, the alternating current is rectified by diodes, and then stored in a capacitor, and then taken out as electricity. Such a technology has been proposed in JP-A-7-107752.
In the power generation unit using such technologies, when a force stronger than the assumed force is applied to the cantilever to thereby excessively swing the cantilever, the cantilever might collide with a peripheral member to thereby be damaged. In order to prevent the above, there has been proposed a technology of providing an elastic body to an inside wall of a housing for housing the cantilever to thereby absorb the impact caused when the cantilever collides with the inside wall of the housing (JP-A-2003-218418).
However, in the technology of the related art proposed in the document, since it is required to prepare a space for disposing the elastic body, there is a problem that it is difficult to sufficiently miniaturizing the power generation unit.